button battery cr1620.Analysis of Explosion Types of Lithium Batteries

　　The types of explosion in battery cells can be classified into three types: external short circuit, internal short circuit, and overcharge. The exterior here refers to the exterior of the battery cell, including short circuits caused by poor insulation design inside the battery pack. When a short circuit occurs outside the battery cell and the electronic components fail to cut off the circuit, high heat will be generated inside the cell, causing some electrolyte to vaporize and propping up the battery shell. When the internal temperature of the battery reaches 135 degrees Celsius, high-quality separator paper will close the fine pores, terminate or almost terminate the electrochemical reaction, cause a sudden drop in current, and the temperature will slowly decrease, thereby avoiding explosion. However, if the closing rate of the pores is too poor, or if the pores do not close at all, the diaphragm paper will cause the battery temperature to continue to rise, causing more electrolyte to vaporize, ultimately breaking the battery shell, and even increasing the battery temperature to cause the material to burn and explode.

　　The internal short circuit is mainly caused by the burrs of copper and aluminum foils penetrating the diaphragm, or the dendritic crystals of lithium atoms penetrating the diaphragm. These small needle shaped metals can cause micro short circuits. Due to the fact that the needle is very thin and has a certain resistance value, the current may not be very high. Copper aluminum foil burrs are caused during the production process, and the observed phenomenon is that the battery leakage is too fast, which can be mostly detected by the cell factory or assembly factory. Moreover, due to the small burrs, they can sometimes be burned off, causing the battery to return to normal. Therefore, the probability of explosion caused by micro short circuits in burrs is not high. This statement can be seen from the fact that there are often defective batteries with low voltage shortly after charging in various battery cell factories, but there are few incidents of explosions that receive statistical support. Therefore, the explosion caused by internal short circuits is mainly caused by overcharging.

　　Because after overcharging, needle like lithium metal crystals are everywhere on the electrode, puncture points are everywhere, and micro short circuits are happening everywhere. Therefore, the temperature of the battery will gradually increase, and finally the high temperature will cause the electrolyte to gas. This situation, whether it is due to excessive temperature causing material combustion and explosion, or the shell being first broken, causing air to enter and undergo intense oxidation with lithium metal, is the end of the explosion. However, the explosion caused by internal short circuits caused by overcharging may not necessarily occur at the time of charging. It is possible that consumers will terminate charging and take their phones out of the house before the battery temperature is high enough for the materials to burn and the gas generated is not enough to break through the battery casing. At this point, the heat generated by numerous micro short circuits slowly increases the temperature of the battery, and after a period of time, an explosion occurs. The common description among consumers is that when they pick up their phone, they find it very hot, and after throwing it away, it explodes. Based on the types of explosions mentioned above, we can focus on preventing overcharging, preventing external short circuits, and improving the safety of the battery cell. Among them, overcharging prevention and external short circuit prevention belong to electronic protection and are closely related to battery system design and battery assembly. The key to improving the safety of battery cells is chemical and mechanical protection, which is closely related to battery cell manufacturers.

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